Using the Festool Domino with Narrow Material by Cary Swoveland ([email protected]) May 2008 1. A Truly Marvelous Invention Anyone who has used Festool’s Domino cannot help but be impressed with the concept, design and construction. In the world of woodworking tools, I know of no other machine that represents such an engineering tour de force. It holds down the #1 spot on my “cool tool” list. But is it perfect? Could the design be improved? There is one area where I think the tool falls short, and that is cutting mortises in relatively narrow material (say, material less than about 4” wide). The problem relates to the positions of the retractable registration pins on each side of the cutter. To cut a mortise in each of two boards to be joined, one often snugs-up one of these pins to an edge of each board. This ensures that the center of the mortise will be 37mm from the edge of the board. The problem is that when cutting a mortise in the end of a relatively narrow board, registering the pin against one side can result in part of the mortise being cut from air. With slightly wider boards, there can be a similar problem when cutting the second of two mortises. There is a simple solution to this problem, and I hope the Festool designers are listening. (OK, I’m sure they’ve thought of this). I would like the Mark II version of the tool to have side-to-side-adjustable registration pins (with detents). In the meantime, we must make do, which is what this paper is about. 2. Spacers Domino owners have all dealt with the “narrow board” problem in one way or another. One approach is to simply mark mortise centerlines on the boards and then carefully align the Domino to the centerlines before cutting. This works pretty well, but sometimes it results in the fit of the joint being a tad off. A variant of this approach is to cut one of the two mortises oversize in width, but then we cannot depend on the domino to line up the boards at the joint. Another approach is to place a spacer between the pin and the edge of the board. This ensures that the joint will fit properly, but it requires that a spacer be cut to the proper width, and the latter sometimes requires a bit of basic math. Also, a third hand may be needed to hold the spacer in position while making the cut. Festool sells an accessory for the Domino called the “Trim Stop”. This is used to hold narrow pieces in place while mortises are being cut. It is designed to cut at marked centerlines, not to cut both pieces being joined from reference points. This paper is about systemizing the spacer approach. I have constructed a set of eight spacers, and prepared tables that show which spacer to use, depending on the type of joint (90-degree butt joint or miter joint), the width of the board, the number of dominos used (one or two), and, where two dominos are used, the spacing between them (more on that later). The eight spacers are shown in Photo 1. The 13mm spacer is shown in use in Photo 2. I made mine from phenolic, but any durable material could be used, such as hardwood, brass, aluminum or steel. The dimensions of the eight spacers are given in Table 1. The “size” of each spacer— which I’ve written on the Photo 1: Domino spacers. spacer—is the distance between the edge of the board abutting the spacer and the near edge of the Domino’s registration pin. In Photo 2, the spacer offsets the Domino’s registration pin 13mm from the edge of the board. The spacers I’ve selected range in size from 4mm (about 5/32”) to 25mm (about 1”). When I suggest using the 0mm spacer, I mean that no spacer should be used (i.e., one of the Domino’s registration pins should be placed against the edge of the board in the conventional way). Photo 2: Domino spacer in place for cut. Table 1. Spacer Sizes and Dimensions (mm) Size (Pin Offset from edge) 25 22 19 16 13 10 7 4 0 Overall Width 55 49 43 37 31 25 19 13 N/A Edge to Mortise Centerline 12 15 18 21 24 27 30 33 37 1. Spacers are 5mm thick. 2. Holes in spacers are 5mm in diameter, centered horizontally, with center 6mm from the top of the spacer. The diameter of the hole in each spacer is the same as the diameter of the Domino’s registration pins, 5mm. The overall width of each spacer is therefore twice the spacer size, plus 5mm. The height and thickness of each spacer is arbitrary. Notice that the spacers have a rabbet at the top. This is so that the lip will slide under the Domino’s fence, holding the spacer snugly in place. This can be seen in Photo 2. I made the spacers 5mm thick at the top (approximately how far the Domino’s registration pins extend from the face of the machine) and 9mm thick at the bottom. Each spacer should be tall enough to permit a line to be scribed 2 on it that shows the offset from the edge of the board to the middle of the mortise to be cut (explained below). I made my spacers about 50mm tall. The center of each hole should be no more than 8mm from the top of the spacer. Anything more can restrict the position of the height of the Domino’s adjustable fence. I suggest 6mm. The distance from the center of the hole to the edge of the lip is 10mm. Therefore, if you drill the hole centered 6mm from the top of the spacer, the rabbet should be 16mm (6mm + 10mm) wide. You may need to sneak up to the width of the rabbet, to achieve a good fit. If you examine Photo 1 carefully, you will see that there is a horizontal line scribed on each spacer. (There are two such lines on the 25mm spacer—I’ll get to that momentarily.) The distance from this line to the bottom of the spacer is the same as the distance from the registration edge of the board to the middle of the mortise being cut. Those distances are shown in the last line of Table 1. These scribed lines are helpful when making “T-type” joints, as shown in Photo 3. To cut a mortise in Photo 3: Marking position of T-type joint. the face grain of the board lying flat, first place the vertical board in the desired position, and mark the registration edge with a pencil, as shown. (The checkmarks provide optional registration information. See the inset on the next page for an explanation.) The next step, shown in Photo 4, is to mark the centerline of the mortise on the end of the board. This is done by lining up the Photo 4: Marking centerline of mortise. line drawn in Photo 3 with the scribed line on the spacer that will be used to mortise the vertical piece. The Domino can now be positioned for the cut by lining up its centerline with the mortise centerline just scribed, as shown in Photo 5. The second line scribed on the 25mm spacer—the one nearer the top—is for use in making a T-type joint when no spacer is used. The distance from this line to the bottom of the spacer is 37mm. Photo 5: Aligning Domino to centerline marked on edge of board. In Photo 2, you can see that the material being cut contacts three solid surfaces. This makes it easy to make fast, accurate cuts to very narrow boards—just clamp the board, hold it against the three surfaces and plunge. My Mark I version of the spaces did not have the lip, so care 3 had to be taken to keep them upright and keep them from falling off the registration pins. Adding the lip overcame both problems.1 Tip: Use Registration Marks After deciding how one or more mortises are to be cut, it is easy to become confused and cut a mortise in the wrong location. This problem can be easily avoided. The key is to observe that the Domino is always positioned using two registration surfaces, or one surface and one line. Ambiguity can be avoided by simply marking the two registration points on each of the boards being joined, as I have done in Photos 3 and 6. (You may wish to use a soft pencil, rather than the large-tip permanent marker I used for these photos.) If presented with a board with two such registration marks, there is only one way to position the Domino for the cut that is consistent with those marks. Photo 6: Marking Domino registration faces. I picked up this suggestion from the Dowelmax user’s guide (that product being #2 on my “cool tool” list). I have considered two types of joints—90-degree butt joints and miter joints—and for each I’ve considered using one or two dominos. Recall that the Domino allows the choice of what may be regarded as a snug, loose or very- loose side-to-side fit for dominos. A snug fit is appropriate when a single domino is used, and is also appropriate for the first mortise cut when two dominos are used.